1. Field of the Invention
This invention relates to a bellows pump used as a pressurized pump for pumping fluid such as gasoline.
2. Prior Art
A publication of Laid Open Japanese Patent Application No. 321781 (1992) has disclosed a bellows pump 9 as shown in FIG. 5. The bellows pump 9 is composed of a first work chamber 91 for admitting fluid, a second work chamber 92 for storing work fluid, a bellows 93 for parting a cheer space into the first work cheer 91 and the second work chamber 92, a piston 94 which moves in a reciprocative manner up to or down from the second work cheer 92 and a work fluid cheer 95. The bellows pump 9 has an oil passage 96 formed therein through which the second work chamber 92 communicates with the work fluid chamber 95 in the vicinity of a bottom dead center of the piston 94.
Referring to FIG. 5, reference numerals 971 and 972 designate a drive shaft and an eccentric cam, respectively for driving the piston 94 up and down. Reference numerals 981 and 982 designate check valves mounted at an inlet port and an outlet port, respectively for limiting the fluid flow to one direction.
The bellows 93 contracts and expands accompanied with the reciprocative motion of the piston 94, by which the fluid is pumped from an inflow channel 985 to an outflow channel 986 under pressure. With this conventional bellows pump 9 if the cycle count of the piston 94 is kept constant, the flow rate "Q" of the fluid becomes constant.
However several problems are associated with the aforementioned bellows pump 9. Bubbles generally intrude into the work fluid either spontaneously or curing assembly of the pump, and these bubbles remain in the second work chamber 92. The bellows pump 9 has a structural difficulty in releasing those bubbles out of the second work chamber 92, thus hindering the pump from performing appropriately or even increasing liabilities of damaging the pump.
Assuming that the bellows pump 9 is used as a fuel pump for an automobile, since the flow rate Q of the fluid is defined by the cycle count of the piston irrespective of the engine load, the outflow rate of the fuel will be excessive at a low engine load, resulting in further degradation of the pump performance. Therefore it is highly required to keep a bellows long-lived for a prolonged service life of the bellows pump. It is also necessary to reduce the bellows pump size for increasing the flow rate.